On 19 Nov 2010, at 7:04am, Yang wrote: > when I create a db on a file system, I guess a query process
Wait ... are you talking here about creating a new database file or querying one what already exists ? > has to go > through 2 levels of seeks ? > first sqlite finds the B-tree node that stores the index to the file > offset of my desired record, then sqlite uses that offset to make > syscall seek(offset), > then Kernel consults the FS implementation to find from its OWN > B-tree (for example in ext3 fs ) the block location of that offset. Assuming that you're using a FS that uses B-trees, nodes, and indices (many don't), that's a fair summary of what happens. But SQLite runs fine on many embedded systems that use linked lists instead of B-trees, or don't use nodes, or have databases stored in non-writable sequential memory. > innodb allows creating a db on a raw disk partition, can we do the > same on sqlite? No. You need a file system of some kind. Or, at least, your operating system needs to be able to address your storage using file-system calls, not storage-structure calls. > I tried directly creating a db on ramdisk, failed: > > javasqlite-20100727# sqlite3 /dev/ram0 You didn't tell it what to call the database, just where you wanted it. I think you want something like # sqlite3 /dev/ram0/myDatabase.sqlite There's no reason this shouldn't work if your drivers and your version of *n*x /fully/ support the use of /deb/ram0 for file storage, including support for locking calls. Works fine under Mac OS X, by the way. But SQLite does provide its own way of creating a database in memory. See http://www.sqlite.org/inmemorydb.html So you'd use something like # sqlite3 :memory: Of course, that database will be visible only to the process that creates it. Which means that if you use the command-line tool to create it it will effectively disappear as you quit the command-line tool. If you're using Linux or a Unix that supports it, you can also look into the shared memory filesystem 'tmpfs'. I haven't tried it, but this should also support SQLite without any problems. Simon. _______________________________________________ sqlite-users mailing list sqlite-users@sqlite.org http://sqlite.org:8080/cgi-bin/mailman/listinfo/sqlite-users
